Apparatus for forming a dimensionally stable anode

ABSTRACT

The specification and drawings disclose an anode for use in electrolytic cells, as well as a method and apparatus for forming the same. The anode is characterized in that its anode surfaces are formed from two sheets of metal having the same configuration and joined to an anode riser such that all weld joints are symmetrically located relative to the axis of the riser. The disclosed method involves a sequence of clamping all components during welding and maintains the various surfaces planar to eliminate warpage. The disclosed apparatus permits the various steps of the method to be carried out simply and rapidly.

United States Patent 1191 Olson et al.

3158a AVAILABLE. COPY [111 [451 July 15, 1975 1 APPARATUS FOR FORMING ADIMENSIONALLY STABLE ANODE [73] Assignee: Diamond Shamrock Corporation,

Cleveland, Ohio [22] Filed: June 11, 1973 [21] Appl. No.: 368,843

[52] US. Cl. 219/80; 219/102; 219/158; 219/161; 269/43; 269/156 [51]Int. Cl B23k 11/00 [58] Field of Search 219/80, 83, 102, 158, 161;269/43, 44, 156, 237

[56] References Cited UNITED STATES PATENTS 2,364,689 12/1944 Brooks269/237 X 2,464,656 3/1949 Sasgen 269/237 X 3,270,180 8/1966 Morley etal. 219/83 X 3,288,978 11/1966 Trygar 219/80 3,632,497 l/1972 Leduc204/263 3,661,757 5/1972 McLean 204/290 F Primary Examiner-J. V. TruheAssistant Examiner-N. D. l-lerkamp Attorney, Agent, or Firm-Fay & Sharpe[5 7] ABSTRACT The specification and drawings disclose an anode for usein electrolytic cells, as well as a method and apparatus for forming thesame. The anode is characterized in that its anode surfaces are formedfrom two sheets of metal having the same configuration and joined to ananode riser such that all weld joints are symmetrically located relativeto the axis of the riser. The disclosed method involves a sequence ofclamping all components during welding and maintains the varioussurfaces planar to eliminate warpage. The disclosed apparatus permitsthe various steps of the method to be carried out simply and rapidly.

6 Claims, 14 Drawing Figures MIENEEQJUL I 5 I975 SHEET FIG. 3

APPARATUS FOR FORMING A DIMENSIONALLY STABLE ANODE BACKGROUND OF THEINVENTION The subject invention is directed toward the art ofelectrolytic cells, especially alkali metal chlorate or bypochlorite anddiaphragm-type chlor-alkali cells and, more particularly, to an anodeassembly for use in such cells and a method and apparatus for formingthe same.

Cells used for electrolysis of alkali metal halide brines usually employa perforated metallic cathode. In chlor-alkali cells, a fluid-permeablediaphragm overlies the cathode and permits hydraulic flow of electrolytefrom the anode chamber through the diaphragm and cathode into thecathode chamber.

Somewhat recently, dimensionally stable anodes have been developed foruse in these cells. For example, US. Pat. No. 3,591,483 to Richard E.Loftfield and Henry W. Laub describes several embodiments ofdimensionally stable anodes and methods and apparatus for efficientlyand simply mounting the anodes.

In general, the anodes described in the noted patent normally comprisean anode riser or conductor bar which supports members having anextended electrically conductive surface. The surface can comprise anyof several materials which have a sufficiently low chlorine overvoltageand which are chemically inert to the electrolyte and resistant to thecorrosive conditions in the cell. The many possible materials which canform the electrically conductive surface are discussed at length in thepatent but, typically, comprise alloys of platinum group metals, oxidesthereof, and mixtures of the metals and oxides.

The electrically conductive surface is normally supported from a sheetor member of a valve metal or alloy thereof; e.g., a film-forming metalsuch as titanium, tantalum, zirconium, niobium and the like. In currentcommercial embodiments, the electrically conductive surface is supportedon perforated or foraminous sheets, expanded metal of titanium.Typically, two of the sheets are joined in parallel on opposite sides ofthe anode riser. The anode riser itself is normally a titanium-cladcopper electrode. In an attempt to maintain parallelism and flatness ofthe sheets, as well as to insure structural rigidity and integrity,various types of cross braces and the like have been joined between thesheets. Generally, the components making up the anode assembly,including the braces, are joined by Welding.

In order for the anode assembly to function satisfactorily, it must havecertain mechanical-structural char acteristics in addition to thechemical and electrical characteristics discussed in the aforementionedpatent. For example, the sheets supporting the electrically con ductivesurface must have a high degree of flatness. And, the flatness, must bemaintained throughout extended periods of operation. This is requiredbecause irregularities in the surface vary the spacing between the anodeassembly and the associated cathode assemblies. As a consequence, thereare variations in current flow and reductions in the overall efficiencyof the cell. Closely associated with the surface flatness requirement isthe necessity for extreme parallelism and uniformity of spacing betweenthe sheets of the anode assembly. Variations in these parameters havethe same general effect on cell performance as lack of flatness.

In addition to the required dimensional uniformity, the joints and/orbonds between the various components must exhibit uniform electricalconductivity as well as structural strength. This has best been achievedby joining the components with a series of closelyspaced spot welds.However. the difficulties encountered in welding the assemblies havebeen substantial. First, titanium is inherently difficult to weld.Secondly, the presence of the electrically conductive surface of oxidesgreatly increases the welding difficulties. Moreover, the weldingoperation itself tends to result in warpage in the assembly.Consequently, the assembly must be straightened following the welding.In most instances, this has been a time-consuming manual operation.

The addition of internal braces or cross members between the sheets inan attempt to reduce the warpage problem merely produced furthermanufacturing problems with little or no lessening of warpage ormechanical distortion problems.

BRIEF STATEMENT OF THE INVENTION The subject invention provides adimensionally stable anode assembly and method and apparatus for formingthe same which overcomes the above-discussed problems.

In general, the preferred anode assembly comprises at least onegenerally cylindrical anode riser member having a pair of metal sheets,typically foraminous, joined to generally diametrically opposite sidesthereof. Each sheet has a major, generally planar, extent with first andsecond spaced edge portions with each joined to the riser member suchthat their respective planar extents are parallel and the first edgeportion of each is generally parallel to and aligned with the secondedge portion of the other. The second edge portion of each sheet is bentto have an integral leg portion extending generally toward the firstedge portion of the other sheet. Each leg portion terminates in a flangeextending parallel to the first edge portion of the second sheet andjoined thereto.

Preferably, and in accordance with a more limited aspect of theinvention, the flange portions are joined to a first edge of theassociated sheet by a closelyspaced series of spot welds. Additionally,the sheets are preferably also joined to the riser by a similar seriesof spot welds.

There are several advantages obtained from the described construction of'the anode assembly. First, only two different major components arerequired for its construction. That is, the riser and the formed sheets.Because of the arrangement, the two formed sheets can have an identicalshape. Secondly, the assembly can be made with all weld lines or spotslocated symmetrically about all planes which contain the axis of theriser. It is believed that this tends to reduce or eliminate warpageencountered following welding of prior designs. Thirdly, reconditioningof the assemblies (i.e., cleaning and applying a new electricallyconductive surface to the assembly) is substantially simpler because theunit does not require internal braces, reverse bends or unusual joints.Additionally, the absence of internal cross members or the like isbelieved to make it easier to hold the required surface flatness, aswell as making it easier to return the assembly to its properdimensional relationships following misuse or damage during use.

In addition to the structural and manufacturing advantages discussedabove, the structural arrangement permits the use of an improved methodof fabricating the assemblies. According to a further aspect of theinvention, the preferred method includes the steps of:

a. positioning the pair of sheets and the riser member in the relativerelationship described above;

b. placing rigid platen members within the assembly to extend betweenthe planar extents of the two sheets and between the leg portions andthe riser;

c. clamping the assembly between rigid, planar, external platenspositioned to leave exposed those portions of the assembly which are tobe joined; and, thereafter,

d. joining the sheets to the riser, and the second edge portion of eachsheet to the first edge of the other sheet by welding.

Preferably, the welding is accomplished by progressively spot welding aclosely and relatively uniformlyspaced series of points along theassembly and parallel to the riser. Additionally, it is preferred thatthe leg portions also be clamped or otherwise rigidly held throughouttheir length during welding.

It has been found that by having the assembled components nearly totallyenclosed by clamping platens with substantially all surfaces rigidlyheld in position throughout the welding operation, the resultingstructure has a higher degree of flatness and parallelism than waspreviously obtainable.

A further aspect of the subject invention concerns apparatusparticularly suited for carrying out the noted method. In general,apparatus of the type contemplated includes a clamping platen assemblycomprising three platen units. Each platen unit comprises two platenmembers spaced by a longitudinally-extending gap which extendscompletely through the respective unit. The three units are mounted injuxtaposed, stacked relationship with their longitudinal gaps inalignment. The mounting means include means which permit the platenunits to be moved between a first clamping position and a second spacedposition for loading and removal of the assembly and components.

The platen units are sized so that the major areas of the sheets of theanode assemblies are engaged and clamped 'while the joint areas areexposed for welding. The intermediate platen unit is arranged so thatthe anode riser is closely received in the longitudinal gap with theplaten members of the intermediate unit substantially completely fillingthe space between the anode riser and the leg portions of the sheets.

Preferably, and in accordance with a more limited aspect, the platenmembers making up the intermediate platen unit preferably includemovable clamp bars which can be actuated laterally to clamp the legportions of the sheets against fixed stops associated with the platenassembly. These clamp bars determine the width and lateral contour ofthe assembly and, with this arrangement, all portions of the anodeassembly are rigidly held during the welding operation.

Desirably, the clamping platen assembly is associated with three sets ofspot welding electrodes so that upon indexed, relative movement betweenthe electrode and the platen assembly in a direction longitudinally ofthe assembly, all weld joints will be made somewhat simultaneously byproviding relative movement between the electrodes and the assembly.Preferably, and in accordance with the preferred embodiment, the platenaspressure. This relationship will be discussed at some length in thedetailed description of the invention.

Briefly, it has been found that these parameters are somewhat criticalif satisfactory welds are to be obtained. In order to obtain the closeand constant current level required, thespot welding electrodes arefired sequentially so that only one is fired at any one point in time.Moreover, the contact pressure between the electrodes and the componentsis maintained somewhat higher'than would be expected.

OBJECTS OF THE INVENTION A primary object of the invention is theprovision of a dimensionally stable anode construction which can bemanufactured to required dimensional tolerances easier than prior artconstructions.

Another object is the provision of an anode construction which uses aminimum number of components to achieve a structure in which the jointsare symmetrically located relative to the center axis of the anode.

Still another object is the provision of method and apparatus by whichanodes of the type discussed can be produced with substantial structuralintegrity.

A further object is the provision of a method and apparatus for forminganodes of the type described which overcomes problems previouslyencountered with respect to warpage and dimensional tolerancevariations.

Yet another object is the provision of an apparatus for totallyenclosing and clamping all major components of the anode assembly duringthe welding.

A further object is the provision of a method and ap paratus wherein allplanar surfaces of the anode assembly are maintained rigidly in positionthroughout the welding operation.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects andadvantages will become apparent from the following description when readin conjunction with the accompanying drawings wherein:

FIG. 1 is a pictorial view of an anode assembly formed in accordancewith the subject invention;

FIG. 1A is an enlarged view of the circled area of FIG. 1 showing theperforated sheet members used for forming the anode of FIG. 1;

FIG. 2 is a cross-sectional view taken on line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken on line 3-3 of FIG. 1;

FIGS. 4A-4D show the preferred sequence of steps used for forming theanode assembly of FIGS. 1-3;

FIG. 5 is an elevational view showing a preferred welding apparatus forwelding the anode assemblies of FIGS. 1-3; I

FIG. 6 is a side elevational view of a platen clamp assembly usedformaintaining the component parts of the anode assembly in the properrelationship during the welding operation; I

FIG. 7 is an end view of the apparatus shown in FIG. 6 (the view istaken on line 7-7 of FIG. 6);

FIG. 8 is a cross-sectional view taken on line 8--8 of FIG. 6;

FIG. 9 is a partial plan view of the apparatus shown in FIG. 6; and,

FIG. 10 is a cross-sectional view taken on line 10-10 of FIG. 8.

DETAILED DESCRIPTION OF THE DRAWINGS Referring more particularly to thedrawings wherein the showings are for the purpose of illustrating apreferred embodiment of the invention only, and not for the purpose oflimiting same, FIG. 1 shows the overall arrangement of an anode assembly10 of the general type described in US. Pat. No. 3,591,483 to Loftfieldet al. In the subject embodiment, the anode assembly is shown ascomprising an anode riser member 12 which carries and supports metalsheets which carry anode surfaces 14. The anode riser 12 comprises agenerally cylindrical member having a conductor core 16 formed from acopper tube (see FIGS. 2 and 3) which has a titanium cover 18 clad orotherwise applied to the tube. It should be appreciated that thematerials from which the assembly is constructed could vary. Theabove-mentioned patent suggests several material combinations which havebeen found to be suitable. However, titanium is preferred. The upper endof the riser member 12 is closed by a titanium cap member 20 welded orotherwise sealingly joined thereto. The cap member 20 serves to totallyenclose and seal the copper core 16 at the upper end. Positioned aboutthe lower end of the riser '12 is a mounting flange 22. Flange 22 isformed from a titanium alloy and permits the unit to be suitably mountedto a base member not shown but described in the aforementioned patent.Additionally, a threaded copper insert 24 is received in the lower endof riser 12 to provide a means for connecting the assembly to a base.Additionally, but not of particular importance to the subject invention,the lower end portion of the riser 12 is provided with wrench flats 26to facilitate installation and removal of the assembly.

Of relative importance to the subject invention is the overallconstruction and arrangement of the anode sheets and their relationshipto the riser 12. As noted above, the anode sheets could be formed frommany different materials and have a variety'of different types ofelectrically conductive surfaces carried thereon; however, in thesubject embodiment, the anode surfaces 14 are supported by foraminoustitanium sheets, specifically sheets of 0.070 inch titanium metalexpanded or perforated to form a mesh-like sheet best illustrated inFIG. 1A. Although the total open area could vary, in the subjectembodiment, approximately one-half of the total sheet area is open asillustrated in FIG. 1A. Additionally, although not shown in FIG. 1, thesheets which carry the anode surface 14 are preferably uniformlyperforated or open throughout their entire area.

In the embodiment shown, the anode surfaces 14 are carried by two of theperforated or expanded metal sheets which have an identicalconfiguration best illustrated in FIG. 2. Note that a first sheet 28includes a first major planar portion 30 having a first end portion 32and a second end portion 34. The second end portion 34 has formedintegrally therewith a short, bent leg 36. The length of leg 36 issubstantially equal to the outside diameter of the anode riser 12. Atthe other end of leg 36, a continuous tab or flange portion 38 is bentto extend generally parallel to the surface of portion 30. A secondsheet member 40 is formed identically to sheet member 28. It includes afirst major planar portion 30' having a first end 32' and a second end34' A leg portion 36' extends from end portion 34 and terminates in aflange 38.

The sheets 28 and 40 are positioned adjacent the exterior of the anoderiser 12 on diametrically opposite sides thereof. The major extents 30and 30' of the sheets 28 and 40 extend parallel to each other and arejoined to the riser 12 by rows of spot welding 42. As shown, the firstends 32, 32' of each sheet are parallel with and joined to therespective tab portions 38 and 38' of the second ends 34 and 34.Likewise, the ends are joined by separate series of spot welds 44 and46. Preferably, the spot welds are located relatively uniform distancesapart and a sufficient number are provided to join at least half orevery other one of the individual strands of the mesh or expanded sheetto the anode riser or the adjacent sheet.

As discussed earlier, it has been found that anode assemblies, whenconstructed as described, can be maintained to a higher degree offlatness and within relatively rigid tolerance limitations. It isbelieved that this results from the symmetry of the assembly about anyplane which includes the axis of the anode riser 12. Note that all weldjoint lines are symmetrically located relative to one another.Additionally, a minimum number of components sufficient to provide thissymmetry are utilized, and no internal cross braces or the like arepositioned within the unit as has been attempted in certain prior artstructures. Of course, if desirable, in large anodes some braces couldbe added. An additional advantage present with the subject structure isthat it is simpler and easier to recondition; i.e., applying a new oxidecoating to the exterior surfaces of the anode sheets FIGS. 4A-4Dillustrate a preferred sequence of steps which can be used for formingthe anode assembly of FIGS. l-3. In general, as shown in FIG. 4A, thesequence begins by positioning a first sheet 28 on a rigid, flat surfacesuch as platen unit having two platen members 52 and 54 positioned andsized so as to engage substantially all portions of surface 30 exceptthose areas required to be exposed for the welding operation. The anoderiser 12 is placed over the sheet 28 in its desired location andsuitably supported and held in location. Thereafter, as illustrated inFIG. 4C, the second sheet 40 is positioned over the sheet 28 and theanode riser 12. Either prior or subsequent to the location of sheet 40,a second platen unit 56 including relatively rigid, flat platen members58 and 60 is positioned so as to substantially fill the spaces betweenthe sheets 28 and 40 (see FIG. 4B).

Subsequent to the positioning of the sheets and the anode riser, a thirdplaten unit 62 is moved into position against surface 30 of sheet 40.Platen unit 62 similarly includes two platen members 64 and 66 sized andlocated so as to engage substantially the entire surface 30 except forthose areas which must be exposed for performing the welding operation.FIG. 4D illustrates an additional step which is preferred prior to thewelding operation. Namely, the application of a clamping force F to theleg portions 36 and 36 to move them against fixed stops and hold themthroughout the weld ing operation. With all of the platen assembliesclampingly engaging the various surface portions of the anode assembly,the spot welding can be accomplished by producing indexed relativemovement between the platen assembly and three sets of spot weldingelectrodes 68, 69 and 70. Preferably, the welding electrodes 68-70 arelocated in alignment and are operated so that all three rows of spotwelding are accomplished simultaneously or nearly simultaneously.

As is apparent, the above-described operation could be carried out withclamping assemblies of various types. Additionally, the welding could beperformed with different electrode arrangements or with different forms.of relative movement between the electrodes and the platen assembly.However, FIGS. -10 illustrate the preferred form of welding and platenassembly 71 formed according to the subject invention. Referencenumerals corresponding to those used in discussing FIGS. 4A-4D have beenused to identify the major components. The overall arrangement of thepreferred form of platen assembly 71 can best be seen by reference toFIG. 6. Broadly, it includes a lower or first platen unit 50, anintermediate or second platen unit 56, and an upper or third platen unit62. The lower platen unit 50 is defined by a single, relatively rigidmetal plate 72 provided with longitudinally-extending through gaps orrecesses 73-75. The gaps 73-75 effectively divide the plate 72 into twoplaten members 52 and 54. It should be realized that the gaps 73-75 alsoleave exposed those portions of the sheet 28 which are to be engaged bythe lower electrodes of the welding electrode sets 68-70. Additionally,as will subsequently become apparent, the plate 72 serves as the base orsupport for the two upper platen units 56 and 62. Positioned on theplate 72 are suitable wear plates 76 and 77 sized so as to engage themajor portions of the surface 30 except for the exposed areas subject towelding. Carried on plate 72 and connected thereto at its opposite endsare suitable locating blocks 80 and 82 which position the anode risermember 12.

As best shown in FIGS. 6, 8 and 10, the intermediate platen unit 56 iscarried from plate 72 for pivotal movement about an axis 84. As shown,the intermediate platen unit 56 is carried by suitable bearings 86connected to the plate member 72. Broadly, intermediate plate unit 56 isarranged so as to define the two separate plate members 58 and 60discussed with reference to the sequence of operations described in FIG.4A. Specifically, the embodiment shown comprises relatively heavyintermediate support plates 87, 88 and 89 connected at their left-handend by vertical plates 90, 91 and braces 92 (see FIG. 6). The center one88 of the intermediate support plates includes a longitudinallyextendinggap sized so as to freely receive the anode member 12. The upper andlower surfaces of the platen members 58 and 60 are defined by upper andlower plates 94 and 96, respectively, which are positively connected tothe intermediate support members 87-89.

Carried by the intermediate platen unit 56 are a pair of laterallymovable clamp bars 98 and 100. The clamp bars 98 and 100 are arranged toclamp the leg portions 36, 36 of the sheets against fixed stop members102 and 104 carried on the plate member 72 (see FIG. 8). In addition toperforming a clamp function, the bars 98 and 100 serve as conductorsbetween the outer sets of electrodes 68 and during the weldingoperation.For this reason, the outer portions of the clamp bars are preferablyformed from a suitable high conductivity material such as copper.

The means for actuating the clamp bars 98 and could be of many types.However, as best shown in FIG. 10, the subject embodiment utilizes abell cranktype drive mechanism 108 for actuating the clamp bar 98. Asubstantially identical, but mirror image drive mechanism (not shown),is used for clamp bar 100. The description of mechanism 108 is to betaken as equally applicable to the mechanism which drives clamp bar 100.Specifically, the clamp bar 98 is carried at the outer ends of threeslide blocks 110 which are mounted for guided reciprocatory movementbetween suitable sets of guide rollers 112 positioned between the upperand lower plates 94, 96. The slide bars 110 are driven simultaneously bythree separate bell cranks 114 pivotally mounted between the upper andlower plates 94, 96. Movement of the bell cranks 114 is accomplished bya longitudinally positioned drive bar 116 guided for movement by rollers118. The left-hand end of the drive bar 116 is connected with the pistonrod of a fluid cylinder 120 carried on plate 91. As best illustrated inFIGS. 6 and 9, the support plate 72 is cut out as shown at 122 to permitthe cylinder 120 to swing through the support plate to the dotted lineposition of FIG. 6. In this position, the various platen units areseparated, as will subsequently be described, so that the components ofthe anode assemblies can be put into position for welding and removedfollowing the welding operation. As previously mentioned, the clamp bar100 is driven and actuated outwardly in the same manner as clamp bar 98but by a separate fluid cylinder.

Referring to FIGS. 6 and 9, it will be seen that the 1 upper platen unit62 is also mounted for pivotal movement from base plate 72. As shown,suitable bearings in the plates 92 so that pivotal movement of theinter-- mediate or middle platen unit 56 can take place. The

preferred construction for the upper platen assembly.

62 can best be .seen in FIGS. 6, 8 and 9. In general, plate assembly 62includes four longitudinallyextending rectangular bars 134. The twocenter bars 134 are spaced apart a distance sufficient to provide accessforthe upper electrodes of the center electrode set 69. The two separateplaten members 64, 66 are defined by plates 136 and 138 which extendbetween thev bars 134. At the left-hand end (as viewed in FIGS. 6 and 9)suitable bracket plates 139 extend outwardly from the bars and receivethe shaft 132. Across the. right-hand end of bars 134, an angle member140 is welded or otherwise positively joined to rigidly connect them.Referring to FIG. 8, it will be noted that the center two bars 134include guide or positioning blocks 144 which engage the upper half ofthe anode riser 12 to maintain in proper position in combination withthe previously-mentioned locating blocks 82 and 80.

The intermediate and upper platen units 56 and 62 are interrelated sothat they will swing to the dotted line position of FIG. 6 for loadingand removal of the anode assemblies. Note that a bar member extendsthrough the brace plates 92 of platen unit 56. Bar 150 is positioned sothat it engages the left-hand end of plates 139 of platen assembly 62.Thus, when platen unit 62 is swung to its lowered or closed position,the ends of the members 139 engage the bar causing the intermediateplaten 56 to be swung to its closed position. Conversely, upon openingof the platen assembly, the intermediate 56 is permitted to swing to itsdotted line position. The relationship of the bearings for the twoplaten units is such that when they are in the open position, they areseparated as shown.

Many different means could be utilized for locking the platen assembliesin their engaged or clamping position. In the subject embodiment, a pairof cam clamps 154 are mounted on the right-hand end of plate member 72and engage the lip of angle member 140 to clamp it in the closedposition. The details of construction of the cam locks 154 form noparticular part of the invention.

The platen assembly described could be used with many different types ofspot welding apparatus. FIG. illustrates a spot welding pressarrangement which is particularly suited for performing the necessaryspot welding operations when using the subject assembly. As shown, thepress includes a main frame 160 which supports a pivotal frame 162carrying the upper ones of the electrode sets 68-70. The opposite onesof the electrode sets are carried from a base frame which is pivotallysupported from frame 160. Associated with the base 164 is a conventionalball-type drive screw unit 165 and guide rails 166 on which the supportplate 72 is carried. By indexing the drive screw members, the plateassembly is to have required movement past the welding electrodes. Itshould, of course, be appreciated that conventional controls areprovided to interrelate the indexed movement of the platen assembly withthe reciprocatory movement of the welding electrodes.

As is the current practice, the major components of the anode assembliesare formed from titanium having an oxide coating. Substantialdifficulties are generally encountered in attempting to obtain a goodweld between such titanium components. Accordingly, a further aspect ofthe invention concerns the required time, temperature, and pressureexerted by the welding electrodes.

To explain the overall functioning and use of the welding apparatus andthe clamping platen assembly, reference is made to FIGS. 6 and 8. Toload the clamping platen assembly, the cam clamps 154 are released andthe intermediate and upper platen assemblies 56 and 62, respectively,are moved to the open or dotted line position. At this time, a sheet 28is placed in location on the lower platen unit 50, and an anode riser 12positioned in the locating blocks 80, 82. A sheet 40 is thereafterpositioned on the upper side of the intermediate platen unit 56. Itshould be understood that the clamp bars 98 and 100 are in theirretracted position and the leg and tab portions of the sheets areoriented as described with reference to FIGS. 1-3.

After the components have been properly positioned, the platen units areclosed and the cam clamps 154 closed. At this time, the clamp bars 98,100 are actuated outwardly to clamp the leg portions of the sheetsagainst the fixed stops 102, 104. Thereafter, the welding can takeplace.

As mentioned earlier, time, temperature or current, and the pressure arerelatively critical when spot welding the titanium sheets. As anexample, in forming the subject assembly in which the sheets are 0.070inch thick titanium expanded metal sheet and the riser has a copper coreand a titanium coating with an'outer diameter l A. inches, extremelygood weld joints have been achieved using copper electrodes with adiameter of one-fourth inch. Each of the electrode sets engage theassembly with a force in the range of 1,000 pounds to produce a contactpressure from 4,000 to 6,000 psi. Current in the range of 10,000 to13,000 amps. at 6 to 10 volts is supplied to the engaged electrodes for4 cycles or 4/60 of a second.

It should be understood that with varying thicknesses of sheet,variation in the parameters somewhat directly.

with thickness will be desirable. Additionally, because slightvariations in current have the effect of producing substantialvariations in weld quality for material of the same thickness, it hasbeen found desirable to control the spot welding electrodes so that onlyone fires at any one instant so that the load on the current supply iscomparatively constant. This can be accomplished with conventionalcontrols and, accordingly, the means for accomplishing this have notbeen shown. It is also believed important that the welding proceed withall of the welding electrodes positioned in general alignment across theassembly and that they have the same movement relative to the assembly.This assures that the heating and the resulting thermal expansion forceswithin the assembly are constant across the width.

The invention has been described in great detail sufficient to enableone of ordinary skill in the art to make and use the same. Obviously,modifications and alterations of the preferred embodiment will occur toothers upon a reading and understanding of the specification and it isour intention to include all such modifications and alterations as partof our invention insofar as they come within the scope of the appendedclaims.

What is claimed is:

1. A clamping platen assembly for use in assembling dimensionally stableanode assemblies of the type comprising a generally cylindrical anoderiser member and a pair of planar sheet members joined in parallel onopposite sides of said riser member, said apparatus comprising:

first, second and third platen units, each platen unit comprising twoplaten members spaced by a longitudinally-extending gap which extendscompletely through the respective unit;

means for mounting said three units in juxtaposed,

stacked relationship with their longitudinal gaps in alignment, saidmounting means including means for permitting the platen units to bemoved between a first clamping position and a second spaced apartposition;

the gap in said second platen unit being sized to closely receive ananode riser member to extend longitudinally thereof and the thickness ofsaid second platen unit being substantially equal to the diameter of theriser; and,

clamp bar members carried by said second platen unit and actuating meanswithin said platen for .moving said clamp bar members radiallyoutwardly.

2. The clamping platen assembly of claim 1 wherein the second platenunit is mounted for pivotal movement relative to said first and thirdplaten units.

3. The platen assembly as defined in claim 1 wherein said third platenunit and said second platen unit are pivotally mounted from said firstplaten unit.

4. The apparatus as defineditj-inclainj l includingmeans for producingindexed movemcntof said platen the same width dimension perpendicular tosaid gaps and wherein said clamp bars, when actuated outwardly, extendbeyond the width of said first and third platen units.

6. The apparatus as defined in claim 1 wherein said clamp bars areformed from a material having high electrical conductivity.

1. A clamping platen assembly for use in assembling dimensionally stableanode assemblies of the type comprising a generally cylindrical anoderiser member and a pair of planar sheet members joined in parallel onopposite sides of said riser member, said apparatus comprising: first,second and third platen units, each platen unit comprising two platenmembers spaced by a longitudinallyextending gap which extends completelythrough the respective unit; means for mounting said three units injuxtaposed, stacked relationship with their longitudinal gaps inalignment, said mounting means including means for permitting the platenunits to be moved between a first clamping position and a second spacedapart position; the gap in said second platen unit being sized toclosely receive an anode riser member to extend longitudinally thereofand the thickness of said second platen unit being substantially equalto the diameter of the riser; and, clamp bar members carried by saidsecond platen unit and actuating means within said platen for movingsaid clamp bar members radially outwardly.
 2. The clamping platenassembly of claim 1 wherein the second platen unit is mounted forpivotal movement relative to said first and third platen units.
 3. Theplaten assembly as defined in claim 1 wherein said third platen unit andsaid second platen unit are pivotally mounted from said first platenunit.
 4. The apparatus as defined in claim 1 including means forproducing indexed movement of said platen units past a first location;and, spot welding heads mounted at said first location, a first set ofsaid spot welding heads positioned to enter the longitudinal gap in saidfirst and third platen units.
 5. The apparatus as defined in claim 4wherein said first, second and third platen units have substantially thesame width dimension perpendicular to said gaps and wherein said clampbars, when actuated outwardly, extend beyond the width of saiD first andthird platen units.
 6. The apparatus as defined in claim 1 wherein saidclamp bars are formed from a material having high electricalconductivity.